1. Field of the Invention
The present invention generally relates to a fluid-dispensing pump for dispensing a fluid stored inside a fluid-storing portion from a nozzle head set up above the fluid-storing portion by pressing the nozzle head.
2. Description of the Related Art
One such known fluid-dispensing pump, for example, is disclosed in Patent Reference 1. The fluid-dispensing pump described in Japanese Patent Application Laid-open No. 2002-66401 comprises a cylinder disposed at the upper part of a fluid-storing portion; a piston which can reciprocate inside the cylinder; a hollow coupling tube to connect the nozzle head and the piston so that a pressing force applied to the nozzle head can be transmitted to the piston to move the piston downward; a coil spring disposed on the periphery of the coupling tube for giving momentum to the piston in an ascending direction; an inflow valve mechanism for allowing a fluid stored in the fluid-storing portion to flow into the cylinder with an ascending motion of the piston; and an outflow valve mechanism for allowing the fluid flowed into the cylinder to flow out into the nozzle head through inside the coupling tube, with a descending motion of the piston.
According to this fluid-dispensing pump described in Japanese Patent Application Laid-open No. 2002-66401, the contact between the fluid and the coil spring for moving the piston upward can be avoided so that it becomes possible to effectively prevent corrosion of the coil spring or dissolution of metal components even when a coil spring providing strong momentum is used. It also becomes possible to easily remove the metal coil spring upon disposing the fluid-dispensing pump.
However, the fluid-dispensing pump described in Patent Reference 1 does not adopt a structure in which a fluid once flowed out into the nozzle head is restored into a cylinder. Therefore, the fluid once flowed out into the nozzle head remains in the nozzle head until it is pushed towards the dispensing port of the nozzle head by the fluid flowed out into the nozzle head from inside the cylinder next time. Consequently, as the period until the fluid in the cylinder flows out into the nozzle head next time becomes longer, the fluid once flowed into the nozzle head will be exposed to the air outside for a longer period of time, which causes the problem that the nature of the fluid may change. Further, the fluid remaining in the nozzle head may flow outside depending on the direction of the nozzle head.